1. Field of the Invention
The present invention relates to Universal Serial Bus (USB) communication, and more particularly, to a clock regeneration method, an associated reference-less receiver, and an associated crystal-less system.
2. Description of the Prior Art
Typically, the conventional receiver needs an external crystal oscillator, so the architecture thereof is complicated. More particularly, the external crystal oscillator is utilized as a source of a reference frequency, various problems may occur. For example, when the conventional receiver utilizes the external crystal oscillator as the source of the reference frequency, additional terminals and associated Electrostatic Discharge (ESD) protection circuits are needed, and therefore, additional costs are introduced. In addition, regarding the problems of the power consumption of the external crystal oscillator and switching noises, it seems unlikely that there is a good solution in the related art. Additionally, a limitation of the thickness may exist in some applications. For example, the thickness of a chip within a chip card may not exceed 800 micrometers, which is much less than a typical width of the outer shell of the external crystal oscillator, so the external crystal oscillator is not suitable for these applications.
In response to the above problems, some solutions are proposed in the related art. However, some side effects may be introduced. For example, according to the related art, inductance-capacitance oscillators (LC OSCs), resistance-capacitance oscillator (RC OSCs), band-gap reference circuits, and/or passive components are required, causing the process to be complicated and causing the overall cost to be increased. Therefore, a novel method is required for clock regeneration, in order to achieve the best receiver performance without introducing the side effects mentioned above, having no need to utilize any external crystal oscillator.